Jang debuted in 1986 with the Haitai Tigers, going 8 for 42 with two homers. He hit .208 and slugged .377 in 1987. In 1988, he improved to .249 and slugged .527 on the strength of a career-best 26 homers. He was four long balls behind KBO leader Sung-han Kim. He won his first Gold Glove at catcher; in the KBO, the Gold Glove goes to the best overall player at each position, not just the best defender.

Jang fell to .244/?/.386 in 1989 with ten homers. He fell back to single-digit circuit clouts in 1990 when his average was .224 and his slugging .354. In '91, Chae-keun rebounded to .235/?/.414 with 17 homers. He won his second Gold Glove. He then starred in the 1991 Korean Series, hitting .467 with 8 RBI to take Korean Series MVP honors.

The Sungkyunkwan alumnus had his best season in 1992 in average at .264. He slugged .518 and went deep 23 times. He won his third and final Gold Glove. From there, it was down hill. He hit only .178/?/.276 in 1993 and was just 6 for 54 with one home run in 1994.

Moving to the Ssangbangwool Raiders in 1995, Jang hit only .175/?/.310 and retired. Overall, he had batted .228/~.317/.413 in 734 games in the KBO.